1. Technical Field
One or more exemplary embodiments of the inventive concept relate to a memory system and a method of controlling an operation thereof, and more particularly, to a memory system, the performance of which may be improved, and a method of controlling an operation of the memory system.
2. Discussion of the Related Art
A large capacity dynamic random access memory (DRAM) has found increased use in mobile electronic products, e.g., a smart phone. DRAM stores data in memory cells constituted by capacitors. Since capacitors leak charge, data stored in a memory cell of a DRAM may be changed. To maintain the data stored in the memory cell, a refresh operation is performed in which the capacitor is periodically recharged.
In addition, as DRAM process technology continues to scale down, the capacitance of a memory cell becomes smaller and a refresh cycle becomes shorter. Thus, if a DRAM is manufactured without changing its refresh cycle or a time needed to perform a write operation, the yield of the DRAM decreases.
To secure data stored in a DRAM, a refresh time of memory cells having a short data retention time (e.g., ‘weak memory cells’) may be used for all of the DRAM's memory cells. In this case, memory cells having a long data retention time (e.g., ‘normal memory cells’) are refreshed with the refresh time of the weak memory cells. Accordingly, even if most of the memory cells are normal, they are refreshed more often than needed. This results in a large amount of power being consumed to perform a refresh operation such as an auto-refresh operation or a self-refresh operation.
A memory system may be controlled by separately managing weak memory cells. However, it is inefficient to use a memory controller to manage information about these idle cells on which operations, e.g., a read/write operation, are not performed.